WO1989009642A1

WO1989009642A1 - Matrix membrane

Info

Publication number: WO1989009642A1
Application number: PCT/EP1989/000368
Authority: WO
Inventors: P. C. Van Der Kuip
Original assignee: Kuip P C V D
Priority date: 1988-04-07
Filing date: 1989-04-06
Publication date: 1989-10-19
Also published as: EP0439461A1; NL8800889A; AU3359589A

Abstract

Matrix membrane containing molecular sieve particles in a matrix wherein the pores of single molecular sieve particles form passages through the membrane and wherein the molecular sieve particles are essentially statistically distributed throughout the matrix.

Description

MATRIX MEMBRANE

The invention relates to a matrix membrane, a process for it's manufacture, an asymmetric zeolite and a process for the separation of mixtures and the preparation of pure chemicals using the matrix membrane or the asymmetric zeolite.

More in particular the invention relates to a matrix membrane containing molecular sieve particles in a matrix wherein the pores of single molecular sieve particles form passages through t membrane.

Such a matrix membrane is known from NL A 6808526 (N.V. PHILIPS GLOEILAMPENFABRIEK) which describes a matrix membrane which is made by depositing granules of a substance which allows material transport, on a sticky substrate, removing the granules which are not sticking to the substrate, incorporating the granules on the substrate into an artificial resin film which is prepared in situ, removing part of the surface of the film by chemical etching and separating the film from the substrate. As a substance allowing material transport molecular sieves are mentioned but particular attention is given to ion exchange materials and all of the examples relate to such ion exchange materials.

This known membrane has the disadvantage that it is difficult to make because thin films of solids and liquids which are rather delicate have to be prepared and worked. Because the granules are not bonded to the artificial 5. resin the granules are easily removed when the film is mechanically worked, e.g. abraded. In the case of molecular sieves chemical etching of the film is prohibited because the molecular sieves in general are poorly resistant to chemical etching.

Such a matrix membrane is also known from US A 2924630

(R.N.FLECK and C.G. WIGHT) which describes several forms of a zeoli ic membrane.

In the second form a single layer of zeolitic silicate solids is positioned between the elements of a wire mesh. The mesh and solids are then covered with a silidifiable material such as a casting resin or a molten metal, which is allowed to harden. This forms a rigid solid matrix reinforced by the wire mesh in the form of a very thin sheet containing the zeolitic particles. The sheet is then treated by means of an abrasive, by milling or chemical etching to remove the outer layers of each side of the sheet thereby exposing upper and lower surfaces of each zeolithic particle. This known matrix membrane also has the disadvantage that a very thin sheet has to be worked either mechanically or chemically. Although the wire mesh reinforcement is intended to enhance the resistance of the sheet the zeolitic particles tend to be removed in mechanical working or chemically degraded in chemical etching. In "Journal of Membrane Science" 22, 137-146 (1985) an investigation on the diffusion coefficient through a zeolite crystal is described. To obtain this one rather large zeolite crystal of 120 microns is embedded in a layer of epoxy-resin that is 200 microns thick and has a surface of one square centimetre. Both surfaces of the layer are treated with sand-paper untill the zeolite is at the surface. This research technique has the disadvantage that only one 120 micron crystal is used per square centimetre for the required separation and that the membrane has to be prepared by the difficult process of scrubbing it with a fine sand-paper. Another limitation of this membrane is that it has a thickness of 120 microns. Finally, the lack of a support limits the amount of pressure one can exert on the membrane. At the other hand FR A 2079460 (SOCIETE DES USINES CHIMIQUES RHONE-POULENC) describes a matrix membrane in which a zeolite is dispersed in a non porous polymer which has a good permeability to gasses or vapours. Although this membrane does not have to be abraded mechanically or chemically it has the disadvantage that the zeolitic particles are completely covered with polymer. Moreover, the thickness of 1 to 0.1 mm is several times the size of the zeolitic particles. This makes that the molecules passing through the membrane have to permeate through the polymer several times, thus strongly reducing the transport velocity and the possible uses of this type of membrane.

EP A 0154248 (BASF AG) describes membranes of organic polymers containing carrier compounds which are capable or the selective transport of low molecular compounds. As carrier compounds zeolites are mentioned. Preferably, the crystal size is such that the crystals are 5 - 100 micron long and form chanels suitable for transport through the 5 - 100 micron thick membrane. The membranes are prepared by pouring a mixture of the crystals and a solution of the polymer on a microporous support membrane and evaporating the solvent. The zeolitic particles will be covered by polymer because of the way the membrane is prepared. An object of the invention is to provide a new matrix membrane not having the disadvantages of the above, known matrix membranes.

A further object of the invention is to provide a novel process for the manufacture of the matrix membrane according to the invention. A still further object of the invention is to provide novel zeolites which may be used in the membrane according to the invention.

A still further object of the invention is to provide processes for the separation of mixtures and for the preparation of pure chemicals using a matrix membrane according to the invention or the asymmetric zeolite according to the invention.

Still further objects of the invention will be apparent to those skilled in the art from the present description, abstract and claims.

According to the invention the matrix membrane containing molecular sieve particles in a matrix wherein the pores of single molecular sieve particles form passages through the membrane is characterised in that the molecular sieve particles are essentially statistically distributed throughout the matrix. Preferably, the molecular sieve particles have a size that is at least a multiple of the thickness of the membrane. In this way the number of particles offering a complete passage is enhanced. To make the passage through the membrane as short as possible while maintaining sufficient strength the thickness of the membrane preferably is 0.1 - 1000 microns, still more preferably 0.1- 100 microns, especially 5 - 50 microns.

A suitable zeolite crystal dimension for the production of a membrane with a thickness of 5 microns is for example 40 microns. Such a thin membrane can not be prepared by abrasion. To maximise the transport capacity through the membrane it is desirable to choose the ratio of molecular sieve to membrane material as high as high as possible, keeping in mind the requirements for good production and the criterea for sufficient strength. Suitable membranes can be produced from a a mixture that, for example, contains 80 volume % molecular sieve material. The surface of the produced membrane will also be 80 % molecular sieve material.

According to an advantageous form of the matrix membrane, the molecular sieve has one or more catalytically active components, preferably a metal from the platina group.

- ET b

Because of this, the matrix membrane can be used for chemical reactions in such a way that reactions of the formed products with each other or with the starting material are avoided. See in this context : EP - A- 0135169. If wanted, the matrix membrane can, in addition to a catalytically active component, also contain a promotor and/or activator in the molecular sieve.

The molecular sieve in the molecular-sieve membrane can be a zeolite from the following group: Mx/n[ (A102)*(Si02)y] ,mH20

In which: -M is a cation, usually Na+, K+ or Ca++ -n is the valence number of the cation M -x and y are whole, positive integers -m is the number of molecules crystalwater

For example the molecular sieves A or X. Also possible as particles for in the matrix membrane is one of the following natural zeolites, for example chabazite, mordenite, analcite or faujasite. The matrix material can be an inorganic substance, for example a metal like alluminium, or it can be an organic substance, for example a macromolecular compound like epoxy resin. An especially good epoxy resin for the zeolite CaA (5A) is the matrix that is prepared from Epon 812, M.N.A. (methylnorbornen-2,3 T- dicarbonsaureanhydrid C10H10O3 reference FLUKA 68165) and the hardener agent DMP 30 (2,3,6- tris(dimethylaminomethyl)-phenol C15H27N30 reference MERCK 12388) .

In order to improve the bonding of the zeolitic particles to the matrix material it is preferred to use an anchoring agent, in particular a silane compound. By using such an anchoring agent the preferred process for the manufacture of the matrix membrane according to the invention is facilitated.

In, among others, pharagraph 6.6 of "Silane Coupling Agents" from E.P. Plueddemann (1982 Plenum Press, New York) recommendations are made for suitable coupling agents between different sorts of polymers and particles. For reinforcement of the bond between the epoxy/ ineral-surface, the following compounds are recommended:

N-(2-aminoethyl-3-aminopropyl)trimethoxysilane or 3-(N- styrylmethyl-2-aminoethylamino)propyltrimethoxysilane- hydrochloride. The use of a coupling agent for bonding a granular substance in a membrane is known per se from Patent Abstracts of Japan vol.9, no. 317(C-319) (2040) , 12 December 1985. The use of a coupling agent for enhancing the compatibility of hydrophilic silica with a hydrophobic polymer in a water permeable membrane is disclosed in this publication. For support of the membrane both porous and non-porous materials can be used. The support can be either organic or inorganic. The porous support for the produced matrixmembrane has to have such a pore diameter on the side where it touches the membrane that the membrane is sufficiently supported when the membrane is contacted with the pressurised mixture that has to be separated. The porous support can have an asymetrical structure. This can be used to reduce the flow resistance through the support. For an inorganic support one can use for example iron, nickel, alluminiumoxyde or glas. For an organic support one can for example use porous polymer foam or a fiber-fleece. To support a CaA(5A)/epoxy membrane without silane coupling agents that had a thickness of about 1 micron, a porous glass support was used successfully. This support had a pore diameter of about 1 to 1.7 micron.

The invention further provides a process for the manufacture of a matrix membrane according to the invention. The process according to the invention is characterised in that the membrane is cut from a body consisting of a mixture, especially a homogeneous mixture of the molecular sieve particles and the matrix material. EP A 0180200(SUZUKI HIROSHI) describes in example 1 the introduction of 75 A zeolite ZSM 5 particles into the pores of VYCOR 7930 porous glas (1 mm thickness) . When a sample is shaved off from one surface by knife the crystallinity is confirmed by x-ray powder diffraction. Obviously a sample of crystals is meant and not the cutting of a 1 mm glass sheet by means of a knife.

The cutting of the composite to obtain the membrane can, for example, be done with a glass knife, with a metal knife, with a knife made from a composite of a metal and an inorganic additive, with a diamond, with a knife that contains diamond on the cutting edge, with a laser, or with a crystal knife. Cutting can be straight, a method that produces flat membranes that have a surface that is limited to the length of the knife and the dimentions of the composite block. Cutting is also possible by using a rotation cutting technique, known from the production of vineer from wood. In this technique, the knife is held against a rotating cylinder of zeolite-matrix mixture. In this case, the membrane surface is only limited by the length of the knife. The matrix membrane according to the invention can be used for all those applications known for molecular-sieve membranes, for example those described in JP 0135069 or the applications described in US A 2924630 or the application described in NL A 6808526.

The invention further provides a process for the production of an asymetrically ion-exchanged zeolite crystal in the membrane. To obtain this, all the ions in the cages of the zeolite are removed or exchanged for smaller ions. This way, the pores in the zeolite crystal are bigger, thus facilitating the transport of molecules through the pores. Then, one side of the membrane is 0

brought in contact with a solution or gaseous mixture (in the case of, for example, chemical vapour deposition) that exchanges the smaller ions back to the larger ones (or puts back the ions if they were removed) during only a short time thus creating asymmetric pores in the zeolite.

The invention further provides a process for the production of asymmetrically ion-exchanged zeolite crystals for the use in , for example, pressure swing adsorption units. To obtain these crystals, all the ions in the cages of the zeolite are removed or exchanged for smaller ions. This way, the pores in the zeolite crystal are bigger, thus facilitating the transport of molecules through the pores. Then, the crystals are brought in contact with a solution or gaseous mixture (in the case of, for example, chemical vapour deposition) that exchanges the smaller ions back to the larger ones (or puts back the ions if they were removed) during only a short time, thus creating asymmetric pores in the zeolite. The outer cages of the crystal are narrower than the ones located more towards the centre of the crystal. EXAMPLE 1

Matrixmembrane for the separation of branched and unbranched hydrocarbons.

100 ml Epon 812 is mixed, during 15 minutes, with 89 ml of M.N.A. (methyl-norbornen-2,3 dicarbonsaureanhydrid C10H1003 referentie FLUCKA 68165). After this, 2.84 ml DMP 30 (2,3,6- tris(dimethylaminomethyl)-phenol C15H27N30 / /

reference MERCK 12388) was added and again mixing was performed during 15 minutes. 0.5 grams of zeolite 5A was weighted in the mold and approximately 1.0 grams of the prepared resin was added. The contends of the mold were mixed untill a practically homogenous mixture was obtained. The mold consisted of a plastic to which the epoxy resin can not bond. The filled mold was put in a dessicator and in the dessicator the pressure was reduced to 0.05 bar for 6 minutes. Because of this, the air bubbles in the epoxy resin were removed, leaving behind a solid mass.

The pressure in the dessicator was brought to 1 bar and the mold with contents was transferred to a stove and kept at 40 degrees Celcius for 72 hours. The mixture was taken from the mold and placed in a microtome (Tissue-Tek accu-cut AS 500 from the company Lab-Tek) . A 12 millimetre wide glass knife (made with the LKB 2078 Histo KnifeMaker) was used to make membranes with a thickness of 0.5 to 5 microns and a surface of 10 by 30 millimetres. EXAMPLE II Example I was repeated with this difference, that the zeolite was pretreated. The zeolite was pretreated with a silane- compound to obtain a surface layer of silane-compound on the zeolite. To do so, a primer was prepared from 50 parts N-(2-aminoethyl-3-aminopropyl)-trimethoxysilane, 50 parts methanol and 5 parts water. After stabilisation during a few hours at room temperature, methanol was added and /2

after that the molecular sieve powder was added. After 5 minutes, the mixture was rinsed with methanol. After this the methanol was evaporated at 30 degrees Celcius. The powder was now ready for addition to the, just prepared, epoxy resin.

EXAMPLE III

Example I was repeated, after which the membrane was placed on a support. As a support, a porous glass plate with a diameter of 25 millimetres and a porosity of 1.0 to 1.7 microns was used. This plate was polished with a fine (one micron particle size) powder/water mixture untill a uniform surface was achieved. The edges of the membrane were glued to the support with epoxy resin and the uncovered surface of the support was sealed off by applying epoxy glue to it. Vacuum was applied to one side of the membrane and the other side of the membrane was placed in a mixture of toluene and n-hexane.

Claims

/iCLAIMS

1. Matrix membrane containing molecular sieve particles in a matrix wherein the pores of single molecular sieve particles form passages through the membrane characterised in that the molecular sieve particles are essentially statistically distributed throughout the matrix.

2. Matrix membrane according to claim 1 characterised in that the molecular sieve particles have a size that is at least a multiple of the thickness of the membrane.

3. Matrix membrane according to claim 1 or 2 characterised in that the thickness of the membrane is 0.1- 1000 micron, preferably 0.1 - 100 micron, especially 5 - 50 micron.

4. Matrix membrane according to one or more of claims 1- 3 characterised in that the molecular sieve particles are bonded to the matrix material by means of an anchoring agent.

5. Matrix membran according to claims 1-4 characterised in that the anchoring agent is a silane compound.

6. Matrix membrane according to one or more of claims 1- 5 characterised in that the molecular sieve contains one or more catalytically active compounds.

7. Matrix membrane according to one or more of claims 1- 6 characterised in that the pores in the zeolite crystals are asymmetric because the outer cages of the crystals holding ions different from the ions located near the centre of the crystals.

8. Matrix membrane according to claim 7 characterised in that only the outer cages of one side of the membrane hold different ions.

9. Asymmetric zeolite characterised in that the outer cages of the crystals hold ions which are different from the ions located near the centre of the crystals.

10. Process for the preparation of asymmetrically ion exchanged zeolite crystals suitable for use in a matrix membrane according to claim 7 characterised in that the asymmetry is achieved by widening all of the zeolite cages by extraction or exchange of the large ions in the cages and subsequently reducing the size of the oute cages by exchange with large ions. ι

11. Process for the manufacture of a matrix membrane according to one or more of claims 1-8 characterised in that the pore volume of the molecular sieve within the membrane is changed in the membrane by means of ion exchange of ions present in the pores.

12. Process for the manufacture of a matrix membrane according to one or more of claims 1-7 characterised in that the membrane is cut from a body consisting of a mixture of the molecular sieve particles and the matrix material.

13. Process for the separation of mixtures for the recovery of wanted components and/or the removal of unwanted components by use of a matrix membrane or a zeolite characterised in that a matrix membrane according to one or more of claims 1-8 or manufactured according to one or more of claims 10-12 or a zeolite according to claim 9 is used.

14. Process for the preparation of pure chemicals by separation and/or chemical conversion using a matrix membrane characterised in that a membrane according to one or more of claims 1-8 or manufactured according to one of claims 10-12 is used.

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S HEET